The present invention relates to a mold which is used to cast a metal article as a single crystal.
Molds for casting single crystal metal articles have previously utilized helical crystal selectors of the so-called "pigtail" type. The casting of single crystal articles utilizing a helical selector is relatively expensive. This expense may be contributed to by a substantial scrap rate. The relatively high scrap rate is, in part at least, due to more than one crystal emerging from the crystal selector into the article mold cavity.
The molds for forming single crystal articles are commonly made by an investment or lost wax process. In this process of making a mold, a wax pattern is first formed. The wax pattern is covered with a layer of ceramic mold material. The wax pattern is removed from the layer of ceramic mold material to leave a space having a configuration corresponding to the configuration of the wax pattern.
The forming of a wax pattern with a helical selector requires relatively complicated tooling or injection molds in which the wax pattern of the helical selector is formed. Single crystal molds having a helical selector are disclosed in U.S. Pat. Nos. 4,475,582 and 4,548,255. A helical selector having a central support element is disclosed in U.S. Pat. No. 4,180,119.